As an antenna, one made by winding a coil (a winding) around an antenna magnetic core is known. The antenna magnetic core has a structure in which a plurality of magnetic thin strips is laminated via a resin layer part, for example. For the magnetic thin strip of the antenna magnetic core, a Co-based amorphous magnetic alloy thin strip or the like is used. A plurality of Co-based amorphous magnetic alloy thin strips is laminated via an adhesive layer (a resin layer part). In order to improve a property as the antenna, there is suggested an antenna magnetic core made by providing a line-shaped mark on a surface of a Co-based amorphous magnetic alloy thin strip and laminating the Co-based amorphous magnetic alloy thin strips with directions of the line-shaped marks being aligned. In an antenna using such an antenna magnetic core, there is a case where the property as the antenna is reduced even though the antenna is fabricated by winding a coil around the antenna magnetic core with no defects in appearance.
There are various factors of reduction in the antenna property as stated above, and as one of the factors, a defect of the resin layer part formed between the magnetic alloy thin strips is conceivable. Conventionally, in forming a resin layer part, there are applied a method of immersing a laminate of magnetic alloy thin strips in a resin liquid, a method of immersing a long-length magnetic alloy thin strip in a resin liquid in the middle of reeling, to form a laminate, and so on. It is conceivable that a defect occurs in the resin layer part due to such a forming method, reducing the property of the antenna. For example, there is a case where an L value or a Q value of an antenna fabricated by winding an antenna magnetic core with no problem in appearance is reduced. A defect of a resin layer part of an antenna magnetic core cannot be judged from appearance, and is a cause to reduce reliability of an antenna.